U.S. patent number 6,706,138 [Application Number 09/931,324] was granted by the patent office on 2004-03-16 for adjustable dual frequency voltage dividing plasma reactor.
This patent grant is currently assigned to Applied Materials Inc.. Invention is credited to Michael S. Barnes, John Holland, Farhad Moghadam, Alexander Paterson, Valentin Todorov.
United States Patent |
6,706,138 |
Barnes , et al. |
March 16, 2004 |
**Please see images for:
( Certificate of Correction ) ** |
Adjustable dual frequency voltage dividing plasma reactor
Abstract
Apparatus and method for processing a substrate are provided.
The apparatus for processing a substrate comprises: a chamber
having a first electrode; a substrate support disposed in the
chamber and providing a second electrode; a high frequency power
source electrically connected to either the first or the second
electrode; a low frequency power source electrically connected to
either the first or the second electrode; and a variable impedance
element connected to one or more of the electrodes. The variable
impedance element may be tuned to control a self bias voltage
division between the first electrode and the second electrode.
Embodiments of the invention substantially reduce erosion of the
electrodes, maintain process uniformity, improve precision of the
etch process for forming high aspect ratio sub-quarter-micron
interconnect features, and provide an increased etch rate which
reduces time and costs of production of integrated circuits.
Inventors: |
Barnes; Michael S. (San Ramon,
CA), Holland; John (San Jose, CA), Paterson;
Alexander (San Jose, CA), Todorov; Valentin (Fremont,
CA), Moghadam; Farhad (Saratoga, CA) |
Assignee: |
Applied Materials Inc. (Santa
Clara, CA)
|
Family
ID: |
25460600 |
Appl.
No.: |
09/931,324 |
Filed: |
August 16, 2001 |
Current U.S.
Class: |
156/345.1;
156/345.23; 156/345.29; 156/345.34; 156/345.44 |
Current CPC
Class: |
H01J
37/32082 (20130101); H01J 37/3244 (20130101) |
Current International
Class: |
H01J
37/32 (20060101); H01L 021/306 () |
Field of
Search: |
;156/345.1,345.23,345.29,345.34,345.44,345 ;216/67,69,71 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
J S. Logan, J. H. Keller, and R. G. Simmons, "The rf Glow Discharge
Sputtering Model," Jan./Feb. 1977, pp. 92-97..
|
Primary Examiner: Norton; Nadine G.
Assistant Examiner: Tran; Binh X.
Attorney, Agent or Firm: Moser Patterson and Sheridan Bach;
Joseph
Claims
What is claimed is:
1. An apparatus for processing a substrate, comprising: a chamber
having a first electrode disposed therein; a substrate support
disposed in the chamber and providing a second electrode in the
chamber; a high frequency power source electrically connected to
either the first or second electrode; a low frequency power source
electrically connected to either the first or second electrode; and
one or more variable impedance elements connected to the first
and/or second electrode, wherein each variable impedance element is
disposed between the first and/or electrode second electrode and an
electrical ground, wherein the variable impedance elements are
adapted to tune a self bias voltage division between the first and
second electrodes.
2. An apparatus for delivering power to a process chamber having a
first electrode and a substrate support forming a second electrode,
comprising: a high frequency power source electrically connected to
the first electrode; a low frequency power source electrically
connected to the first electrode; and a variable impedance element
connected between the substrate support and an electrical
ground.
3. The apparatus of claim 2, wherein the high frequency power
source is adapted to deliver power between about 13.56 MHz and
about 500 MHz.
4. The apparatus of claim 2, wherein the low frequency power source
is adapted to deliver power between about 100 kHz and about 4
MHz.
5. The apparatus of claim 2, wherein the variable impedance element
comprises at least one inductor and at least one capacitor.
6. The apparatus of claim 2, wherein the variable impedance element
comprises at least one inductor and at least one variable
capacitor.
7. The apparatus of claim 2, wherein the variable impedance element
is adapted to tune at least one resonant impedance at a frequency
selected from at least one of the low frequency and the high
frequency.
8. The apparatus of claim 2, wherein the variable impedance element
is adapted to tune a first resonant impedance at the low frequency
and a second resonant impedance at the high frequency.
9. The apparatus of claim 2, wherein the first electrode comprises
a gas distributor.
10. The apparatus of claim 2, wherein the first electrode and the
substrate support are disposed to form parallel plate
electrodes.
11. The apparatus of claim 2, wherein the chamber is configured as
an etch chamber.
12. An apparatus for delivering power to a process chamber having a
first electrode and a substrate support forming a second electrode,
comprising: a high frequency power source electrically connected to
the first electrode; a low frequency power source electrically
connected to the first electrode; and a variable impedance element
connected between the substrate support and an electrical ground,
wherein the variable impedance element is adapted to tune a self
bias voltage division between the first electrode and the substrate
support.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a substrate processing
chamber. More particularly, the invention relates to a method and
apparatus for delivering power to a processing chamber.
2. Background of the Related Art
Plasma etching and reactive ion etching (RIE) have become important
processes in precision etching of certain workpieces such as
substrates in the fabrication of semiconductor devices. The
differences between plasma etching and reactive ion etching, which
generally can be carried out in the same equipment, typically
result from different pressure ranges employed and from the
consequential differences in mean free path of excited reactant
species in a processing chamber. The two processes are collectively
referred to herein as plasma etching. Plasma etching is a "dry
etching" technique and has a number of advantages over conventional
wet etching in which the workpiece is generally immersed in a
container of liquid etchant material. Some of the advantages
include lower cost, reduced pollution problems, reduced contact
with dangerous chemicals, increased dimensional control, increased
uniformity, improved etch selectivity, and increased process
flexibility.
As integrated circuit densities increase, device feature sizes
decrease below 0.25 micron while the aspect ratio (i.e., ratio of
feature height to feature width) of the device features increase
above 10:1. Improved precision of the etch process is required to
form these small device features having high aspect ratios.
Additionally, an increased etch rate is desired to improve
throughput and reduce costs for producing integrated circuits.
One type of plasma etch chamber utilizes two parallel plate
electrodes to generate and maintain a plasma of the process gases
between the plate electrodes. Typically, a parallel plate plasma
etch chamber includes a top electrode and a bottom electrode. The
bottom electrode typically serves as a substrate holder, and a
substrate (or wafer) is disposed on the bottom electrode. The etch
process is performed on a surface of the substrate that is exposed
to the plasma.
Typically, one or more of the electrodes are connected to a power
source. In a particular parallel plate reactor, those electrodes
are connected to high frequency power sources. The power source
connected to the upper electrode is typically operated at a higher
frequency than the power source connected to the lower electrode.
This configuration is believed to avoid damage to materials
disposed on a substrate.
Another parallel plate reactor has two power sources connected to a
lower electrode. The power sources are each operated at different
frequencies in order to control the etching characteristics
resulting on a substrate being processed.
Yet another parallel plate reactor includes three electrodes. A
first electrode is adapted to support a substrate and is connected
to a low frequency AC power source. A second electrode is disposed
in parallel relationship with the first electrode and is connected
to ground. A third electrode (i.e., the chamber body) disposed
between the first and second electrode is powered by a high
frequency AC power source.
Another conventional apparatus provides a single powered electrode
reactor. High and low frequency power supplies are coupled to the
single electrode in an effort to increase process flexibility,
control and residue removal. The single electrode reactor includes
a multistage passive filter network. The network is intended to
perform the functions of coupling both power supplies to the
electrode, isolating the low frequency power supply from the high
frequency power supply and attenuating the undesired frequencies
produced by mixing of the two frequencies in the nonlinear load
represented by the reactor.
A more detailed description of dual frequency parallel plate
reactors can be found in U.S. Pat. No. 4,464,223, entitled "Plasma
Reactor Apparatus and Method," assigned to Tegal Corp., and issued
Aug. 7, 1984; U.S. Pat. No. 5,512,130, entitled "Method and
Apparatus of Etching a Clean Trench in a Semiconductor Material,"
assigned to Texas Instruments, Inc., issued Apr. 30, 1996; U.S.
Pat. No. 4,579,618, entitled "Plasma Reactor Apparatus, assigned to
Tegal Corp., issued Apr. 1, 1986; and U.S. Pat. No. 5,272,417,
entitled "Device for Plasma Process, issued Dec. 21, 1993.
One problem typically experienced in a parallel plate plasma etch
chamber is that material from the surfaces of the top electrode
exposed to the plasma in the chamber is also etched during the etch
process. As the top electrode is eroded by the etch process, the
material property of the top electrode changes and causes
variations of the processing parameters in the chamber, which
results in inconsistent or non-uniform processing of substrates.
Furthermore, the top electrode may have a short useful life and may
need to be replaced frequently, which increases the costs
associated with production of the semiconductor devices.
Therefore, there is a need for a parallel plate plasma etch system
that can substantially reduce erosion of the top electrode and
maintain process uniformity. It would be desirable for the plasma
etch system to improve precision of the etch process for forming
high aspect ratio sub-quarter-micron interconnect features. It
would be further desirable for the plasma etch system to provide an
increased etch rate which reduces time and costs of production of
integrated circuits.
SUMMARY OF THE INVENTION
The present invention generally provides a parallel plate plasma
etch system that can substantially reduce erosion of a top
electrode and maintain process uniformity. The plasma etch system
improves precision of the etch process for forming high aspect
ratio sub-quarter-micron interconnect features. The plasma etch
system also provides an increased etch rate which reduces time and
costs of production of integrated circuits.
In one aspect, the invention provides an apparatus for processing a
substrate comprising a chamber having an electrode, a substrate
support disposed in the chamber, a high frequency power source
electrically connected to the electrode, a low frequency power
source electrically connected to the electrode, and a variable
impedance element connected between the substrate support and an
electrical ground.
In one embodiment, the electrode comprises a gas distributor, and
the electrode and the substrate support form parallel plate
electrodes. The high frequency power source is adapted to deliver
power at a frequency between about 13.56 MHz and about 500 MHz
while the low frequency power source is adapted to deliver power at
a frequency between about 100 kHz and about 20 MHz. The variable
impedance element is adapted to tune a self bias voltage division
between the electrode and the substrate support and is adapted to
tune at least one resonant impedance at a frequency selected from
at least one of the low frequency and the high frequency.
In another aspect, the invention provides a method for delivering
power to a process chamber having a first electrode and a substrate
support forming a second electrode comprising delivering a high
frequency power from a high frequency power source electrically
connected to the first electrode, delivering a low frequency power
source from a low frequency power source electrically connected to
the first electrode, and connecting a variable impedance element
between the substrate support and an electrical ground. In one
embodiment, the method further comprises tuning the variable
impedance element to control a self bias voltage division between
the first electrode and the substrate support. The variable
impedance element may be tuned to provide a first resonant
impedance at the low frequency and a second resonant impedance at
the high frequency.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above recited features, advantages
and objects of the present invention are attained and can be
understood in detail, a more particular description of the
invention, briefly summarized above, may be had by reference to the
embodiments thereof which are illustrated in the appended
drawings.
It is to be noted, however, that the appended drawings illustrate
only typical embodiments of this invention and are therefore not to
be considered limiting of its scope, for the invention may admit to
other equally effective embodiments.
FIG. 1 is a schematic cross sectional view of a processing chamber
according to aspects of the invention.
FIG. 2 is a schematic diagram of one example of a variable
impedance element of the invention.
FIG. 3 is a schematic cross sectional view of another processing
chamber according to aspects of the invention.
FIG. 4 is a schematic cross sectional view of another processing
chamber according to aspects of the invention and including
alternate ground returns for the high frequency and low frequency
RF power.
FIG. 5 is a schematic cross sectional view of another embodiment of
a processing chamber according to aspects of the invention
including a combined low and high frequency power source with
chamber matching.
FIG. 6 is a schematic cross sectional view of another embodiment of
a processing chamber according to aspects of the invention.
FIG. 7 is a schematic cross sectional view of another embodiment of
a processing chamber according to aspects of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is a schematic diagram of one embodiment of a parallel plate
processing system 100 of the invention. The processing system 100
may be attached to a processing system platform and may comprise a
multi-purpose chamber configured to perform a specific process,
such as an etch process. Although the invention is described with
respect to a particular configuration, it is understood that the
invention is applicable in a variety of configurations and designs.
Further, it is understood that the system is a simplified schematic
representation and some aspects that may be part of the processing
system 100 are not shown. For example, actuators, valves, sealing
assemblies and the like are not shown. Persons skilled in the art
will readily recognize that these and other aspects may be
incorporated into the processing system 100.
The process chamber 100 generally includes a chamber body 202
defining a cavity 231 at least part of which is a processing
region. The chamber body 202 includes a chamber wall 204 and a
chamber bottom 206. The chamber wall 204 extends substantially
perpendicularly from the edge of the chamber bottom 206. An opening
230 is formed in the chamber wall 204 and serves to facilitate
substrate transfers into and out of the processing system 100.
Although not shown, a slit valve may be provided to selectively
seal the opening 230. The chamber bottom 206 includes an outlet 208
for exhausting gases from the chamber. An exhaust system 210 is
attached to the outlet 208 of the chamber bottom 206. The exhaust
system 210 may include components such as a throttle valve and a
vacuum pump. Once the opening 230 is sealed, exhaust system 210 may
be operated to draw and maintain a vacuum within the cavity
231.
A plate electrode 236 is disposed at an upper end of the chamber
body 202. In one embodiment, the plate electrode 236 includes a
protective coating 249 which prevents or reduces erosion of the
material of the plate electrode 236 caused by the plasma in the
chamber. The protective coating may comprise a material such as
quartz, sapphire, alumina, SiC, SiN, and Si. Although the chamber
is described having a plate electrode, other chamber designs having
inductive, capacitive, or a combination of inductive and capacitive
plasma sources may also be utilized.
In one embodiment, the plate electrode 236 is a showerhead of a gas
distribution system. In such a configuration, the plate electrode
236 may be part of a lid assembly that is adapted to distribute
gases into the cavity 231. Accordingly, FIG. 1 shows a gas source
246 coupled to the plate electrode 236. The gas source 246 contains
the precursor or process gases to be utilized for processing the
substrate in the chamber. The gas source 246 may include one or
more liquid ampoules containing one or more liquid precursors and
one or more vaporizers for vaporizing the liquid precursors to a
gaseous state.
The plate electrode 236 is connected to a power source 240 which
supplies RF power to the plate electrode for generating and
maintaining a plasma in the chamber. The power source 240 includes
a low frequency RF power source 250 and a high frequency RF power
source 252. The low frequency RF power source 250 is connected to
the plate electrode 236 through a low frequency match network 254
and enhances ion assisted etching at the substrate. The high
frequency RF power source 252 is connected to the plate electrode
236 through a high frequency match network 256 and enhances
dissociation of the process gases and plasma density. Each of the
match networks 254, 256 may include one or more capacitors,
inductors and other circuit components. The low frequency RF power
source 250 may deliver RF power to the plate electrode 236 at a
frequency at or below about 20 MHz while the high frequency RF
power source 252 may deliver RF power to the plate electrode 236 at
a frequency at or above 13.56 MHz. In one embodiment, the low
frequency RF power source 250 delivers RF power to the plate
electrode 236 at a frequency between about 100 kHz and about 20 MHz
while the high frequency RF power source 252 delivers RF power to
the plate electrode 236 at a frequency between about 13.56 MHz and
about 500 MHz. Preferably, the high and low frequencies do not
overlap during operation. That is, the low frequency RF power
source 250 is always operated a frequency below the frequency of
the high frequency RF power source 252.
While the plate electrode 236 acts as a top electrode of a parallel
plate electrode plasma reactor, a substrate support 216 acts as a
lower electrode. The substrate support 216 is disposed in the
cavity 231 and may be any structure suitable for supporting a
wafer, such as an electrostatic chuck or a vacuum chuck. The
substrate support 216 includes a support plate 219 defining a
substrate supporting surface that is generally shaped to match the
shape of a substrate supported thereon. Illustratively, the
substrate supporting surface is generally circular to support a
substantially circular substrate. In one embodiment, the substrate
supporting surface is thermally connected to a substrate
temperature control system, such as a resistive heating coil and/or
fluid passages connected to a heating or cooling fluid system.
The system 100 may include liners or rings that are configured for
various functions. Illustratively, the process system 100 may
include three confinement rings 250A-C. In one embodiment, each
ring is made of nickel, aluminum, or other metals or metal alloys
appropriate for plasma processing, and may also include an anodized
aluminum surface. The rings 250 may be a single piece construction
or a multi-piece construction.
A first ring 250A is disposed about the support plate 219. A second
ring 250B is disposed around the upper electrode. A third ring 250C
is disposed between the first and second rings 250A-B. In
operation, the rings act to confine the plasma in the region above
the substrate between the plate electrode 236 and the substrate
support 216. The rings confine the plasma laterally in the chamber
and minimize losses to the walls of the chamber.
To provide an adjustable voltage division between the top electrode
and the bottom electrode, a variable impedance element 260 is
connected between the substrate support 216 and an electrical
ground or a ground connection. The variable impedance element 260
may include one or more capacitors, inductors and other circuit
components. One embodiment of the variable impedance element 260 is
described below with reference to FIG. 2.
FIG. 2 is a schematic diagram of one example of a variable
impedance element 260. As shown in FIG. 2, the variable impedance
element 260 includes a capacitor C1 connected in parallel to a
series combination of an inductor L and a capacitor C2. In one
embodiment, the capacitors C1 and C2 may comprise variable
capacitors which can be tuned to change the resonant frequency and
the resonant impedance of the variable impedance element 260. A
stray capacitance C.sub.stray, which is parallel to capacitor C1,
may be included in determining the resonant frequency and the
resonant impedance of the variable impedance element 260.
The variable impedance element 260 can be tuned to change the self
bias voltage division between the plate electrode 236 and the
substrate support 216, at either or both of the low and high
frequencies. A low resonant impedance at the high frequency (i.e.,
the frequency at which the high frequency power source is
operating) provides high frequency plasma generation that is either
equal between the plasma sheaths of both electrodes or slightly
enhanced at the upper electrode. A high resonant impedance at the
low frequency (i.e., the frequency at which the low frequency power
source is operating) provides more self bias at the bottom
electrode (i.e., substrate support), even though the substrate
support is not directly connected to or powered by the power
source. The increased self bias at the bottom electrode enhances
the ion acceleration toward the bottom electrode, which provides
improved etching results on a substrate disposed on the substrate
support. Additionally, the increased self bias on the bottom
electrode significantly reduces erosion of the top electrode or the
protective covering on the top electrode.
To perform a plasma etch process, a substrate is transferred into
the process chamber and positioned on the substrate support 216.
The substrate support 216 may be moved into a processing position
with a desired processing distance between the top electrode and
the substrate support surface. The process/precursor gases are
introduced into the chamber through the gas distributor, and a
plasma is generated and maintained for a desired duration to
complete the etch process on the substrate. Plasma etch processes
may be performed utilizing reactive gases, such as O.sub.2,
N.sub.2, Cl, HBr, SF.sub.6, CF.sub.y, C.sub.x F.sub.y, C.sub.x
H.sub.y F.sub.z, NF.sub.3, and other etch precursors, with one or
more inert gases, such as Ar, He, etc. The substrate is then
transferred out of the process chamber.
The following table presents examples of chamber operating
conditions for an etch process performed in one embodiment of a
chamber of the invention.
Processing Parameter Parameter Value Distance between top electrode
and About 0.5 cm to about 10 cm bottom electrode Chamber Pressure
About 20 mT to about 1 Torr Power Density About 1 W/cm to about 20
W/cm Frequency of Low Frequency Power .ltoreq.20 MHz Source
Frequency of High Frequency Power .gtoreq.13.56 MHz Source
FIG. 3 is a schematic cross sectional view illustrating another
embodiment of a chamber configuration and power delivery system. In
this embodiment, the high and low frequency power are delivered to
the substrate support member 216 through the HF match 256 and LF
match 254, respectively. The variable impedance element 260 is
connected to the plate electrode 236, such as a showerhead
assembly, to adjust the RF power delivered to the processing region
231 by controlling the RF ground path impedance for the plate
electrode 236. As the variable impedance is adjusted, the voltage
drop across the processing region 231 changes accordingly. For
example, as the variable impedance is adjusted to lower the
impedance value, the current through the variable impedance
element(s) 260 increases, increasing the voltage drop across the
processing region 231, thereby increasing the RF energy
transmitted. As the variable impedance element is adjusted to a
higher impedance value, the voltage drop across the processing
region 231 decreases, thereby departing less RF energy. In one
aspect, the variable impedance can be adjusted in combination with
the LF match 254 and HF match 256 to establish a desired plasma
density without adversely affecting the HF 256 and LF 254 match
between the RF power generators 250, 252 and the chamber 202. In
one aspect, the tuning impedance of variable impedance element(s)
260 may be adjusted so that the sheath impedance and the variable
impedance element(s) 260 are substantially in series resonance
providing a substantially low impedance path for either the high or
low frequency RF signals. Alternatively, the variable impedance
element(s) 260 can be tuned above or below resonance for either RF
signal to change the amount of RF current flowing through this
electrode to ground.
FIG. 4 is a schematic cross sectional view illustrating another
embodiment of a chamber configuration and power delivery system. In
this embodiment, the high frequency power is delivered from the HF
generator 252 to the plate electrode 236, such as a showerhead, and
the low frequency power is delivered from the LF generator 250 to
the substrate support member 216. An upper variable impedance
element 260B is connected to the upper electrode 236 and a lower
variable impedance element 260C is connected to the substrate
support member 216. In this embodiment, the lower variable
impedance element 260C provides a ground return path for the high
frequency RF components from the HF generator 252 delivered to the
processing region 231 and provides a high impedance path for the LF
generator 250. In addition, the upper variable impedance element
260B provides a ground return path for the low frequency RF
components from the LF generator 250 delivered to the processing
region 231 and provides a high impedance path for the HF generator
252. Thus, the ratio of the delivered high frequency RF power to
the delivered low frequency RF power may be independently adjusted
and matched to the desired process parameters. In one aspect, the
tuning impedance of the low frequency variable impedance element
260C may be adjusted so that the sheath impedance and the lower
variable impedance element 260C are substantially in series
resonance providing a substantially low impedance path for the low
frequency RF signals. In another aspect, the tuning impedance of
the high frequency variable impedance element 260B may be adjusted
so that the sheath impedance and the high frequency variable
impedance element 260C are substantially in series resonance
providing a substantially low impedance path for the high frequency
RF signals. Alternatively, the variable impedance element(s) 260B,
260C can be tuned above or below resonance to decrease the RF
current at these frequencies from flowing through this electrode
and/or change the self bias to this frequency.
In another embodiment illustrated in FIG. 5, an isolated wall
electrode 265 is provided and is connected to a wall tuning element
260A. The plate electrode 236 is adjacent to and horizontally
spaced from the chamber wall 204 using an insulating material 262
selected from insulators such as ceramics, polymers, glass, and the
like adapted to withstand the RF power applied to the plate
electrode 236. The insulating material 262 electrically insulates
the plate electrode 236 from the chamber wall 204 to allow the
plasma to be directed under, and in substantial conformity with,
the plate electrode 236. A wall electrode 265 composed of
conductors such as aluminum, nickel, tungsten, and the like adapted
to receive RF energy, is electrically isolated from the wall 204
and plate electrode 236 by the insulating material 262. The wall
electrode 265 is adjacent to and vertically spaced from the chamber
wall 204 forming an internal wall about processing region 231. A
wall variable impedance element 260A is coupled to the wall
electrode 265, providing an adjustable ground return path for RF
energy proximate the chamber wall 204 from the plate electrode 236.
The wall variable impedance element 260A is adapted to increase or
decrease the RF energy to the support member 216 by providing an
alternate ground path for the RF with respect to the support member
216. In one aspect, the wall variable impedance element 260A, in
cooperation with the wall electrode 265, provides plasma
confinement and control. To confine the plasma, the effective
impedance between the plate electrode 236 and the wall electrode
265 is increased to a value great enough using the wall variable
impedance 260A, to effectively minimize the RF path to ground,
thereby constraining the plasma between the plate electrode 236 and
the support member 216. Thus, the plasma adjacent to the wall is
minimized, reducing the risk of plasma damage to the wall 204.
In another aspect, the plate electrode 236 and the wall impedance
is adjusted to a value low enough to effectively decrease the RF
path to ground impedance, shunting some of the RF power away
between the plate electrode 236 and the support member 216, thereby
decreasing the plasma density. Additionally, the spacing between
the wall electrode 265 and the plate electrode 236 and/or support
member 216 may be adjusted to allow for more or less confinement
and control of the RF energy. Accordingly, the more confinement and
control of the plasma which is realized, the closer the wall
electrode 265 is placed to the plate electrode and/or the support
216.
In another embodiment as illustrated in FIG. 6, the LF matching
network 254 is coupled to the plate electrode 236 and the high
frequency match 256 is coupled to the support member 216. An upper
variable impedance element 260B is coupled to the plate electrode
236. A lower variable impedance element 260C is coupled to the
support member to provide variable RF paths for the high frequency
RF power source 252 and the low frequency RF power source 250,
respectively. Each variable impedance element 260B-C may be
adjusted to provide the proper RF return path as needed to adjust
the voltage and current for each high or low frequency impedance
path. The upper variable impedance element 260B is adapted to
provide a ground return path for the high frequency RF components
of the HF generator 252 and provide a high impedance path for the
LF generator 250. The lower variable impedance element 260C is
adapted to provide a ground return path for the low frequency RF
components of the LF generator 250 and provide a high impedance
path for the HF generator 252. The upper and lower impedance
elements 260B, 260C may be separately adjusted to balance the
amount of energy delivered from each RF generator 250, 252 to the
processing region 231. Increasing the impedance of the lower
variable impedance element 260C decreases the voltage drop across
the processing region, increases the overall chamber impedance with
respect to the LF match 254, and thereby lowers the low frequency
RF current and power delivered to the processing region 231. In
addition, increasing the impedance of the upper variable impedance
element 260B decreases the voltage drop across the processing
region 231, increases the overall chamber impedance with respect to
the HF match 256, and thereby lowers the high frequency RF current
and power delivered to the processing region 231. For example, the
impedance of the upper variable impedance element 260B may be
adjusted to allow more high frequency RF power to be applied to the
substrate support member 216 while the impedance of the lower
variable impedance element 260C may be increased to decrease the
low frequency power delivered to the plate electrode 236. Thus, the
ratio of the delivered high frequency RF power to the delivered low
frequency RF power may be independently adjusted and matched to the
desired process parameters. In one aspect, the tuning impedance of
the upper variable impedance element 260B may be adjusted so that
the sheath impedance and the upper variable impedance element 260B
are substantially in series resonance providing a substantially low
impedance path for the high frequency RF signals. In another
aspect, the tuning impedance of the lower variable impedance
element 260C may be adjusted so that the sheath impedance and the
lower variable impedance element 260C are substantially in series
resonance providing a substantially low impedance path for the low
frequency RF signals. Alternatively, the variable impedance
elements 260B, 260C can be tuned above or below resonance to
reflect RF power back to the chamber as needed.
In another embodiment, as illustrated by FIG. 7, the low frequency
RF power source 250, low frequency matching network 254, high
frequency RF power source 252, and high frequency matching network
256, are combined into a single apparatus to minimize coupling and
connection losses. The HF/LF Generator/Match combination is
connected to the plate electrode. A wall electrode 265 and a wall
tuning element 260A are provided to confine the plasma and minimize
losses of the plasma to ground through the walls 204 of the
chamber. Substrate tuning element 260C is connected to substrate
support 216.
While the foregoing is directed to certain embodiments of the
invention, other and further embodiments of the invention may be
devised without departing from the basic scope thereof, and the
scope thereof is determined by the claims that follow.
* * * * *